Question

I thought the result would be (2**32 - 1)

#include <stdio.h>
int main(){
  unsigned int a = 0xffffffff;
  printf("the size of int a %d\n",a);
  return 0;
}

but it gives me -1, any idea?

Answer 1

You’re asking printf() to interpret that value as a signed integer, whose range is -(2**31) to (2**31)-1. Basically, the high bit is a sign bit. Read about two’s complement.